@Preciousmemory This sounds like a total nightmare, I am sorry this has happened to you.
No judgement on you at all but it doesn't sound like you're remotely equipped skills or experience wise to deal with a dog like this (he is not 'protecting you' even well balanced healthy dogs do not do that. He is protecting himself and it sounds like he is so off balance he is doing so offensively - ie, going out of his way to drive away perceived danger, actually putting himself at more risk to do so - clearly maladaptive, abnormal behaviour. This tends to happen when an already fearful dog is pushed way beyond his ability to cope. ).
He is a long way from needing a trainer, he needs weeks or months to decompress, and then a behaviour modification program following an in depth assessment by a behaviourist. Only once that has worked and you have a relaxed, happy dog, can you even think about training!
You should never have been given a dog like this, and this sort of set up where dogs are not assessed, not given the time they need before moving to a new home and the rescue then has nowhere to put them when the homing fails, is exactly why so many rescue people and behaviour/training people are anti-overseas rescue.
Your options:
1 - out of hours vet, euthanise on the basis that he has bitten several people and you can't keep him safe.
Beaware that you will receive a barrage of shit from the rescue and likely be bad mouthed across social media, with their version of the truth presented as fact.
2 - try calling the police. This dog has now been abandoned with you, you are fearing injury, have already suffered prior injury and the dogs legal owners are refusing to collect in a reasonable time frame. The efficacy of this really depends on how good your local police service is.
I really don't have any better suggestions - unfortunately this is a situation some of us have seen play out over and over, countless times, with dogs effectively dumped with people who cannot cope with them, and threatened that they must keep this dog until some unspecified time when someone might turn up and take it away!
If you still want to try with him, he needs to decompress - a room to himself, limited contact with people and only with a muzzle on. Just do the bare bones of what is necessary, food, somewhere to toilet, drink. I fully appreciate, you may not be able to achieve that!